For more than the past decade, multilateral wells have become increasingly popular. These wells increase the accessibility to formation reserves in oil and gas production fields. A multilateral well is constructed by drilling a main well bore and then drilling branch well bores, or lateral well bores, off of the main well bore into different producing regions of the reservoir. Once drilled, the multilateral well resembles a branch of a fern with lateral branches directed off of the main well bore or stem. These multilateral branch well bores are known to be drilled in both vertical wells and horizontal wells. The primary advantage of multilateral well construction is the ability to drain a much larger portion of the hydrocarbon bearing reservoir with a single well bore from the surface.
Drilling the lateral “legs”, or branch well bores, off of the main well bore commonly requires a device called a whipstock. A whipstock is a long wedge shaped tool that attaches to the well casing and forces or directs the drill string away from the centerline of the main well bore in order to create the lateral well bore. Prior to drilling the lateral or branch well bore, the whipstock is run into the hole and locked in place in the main well bore. The whipstock has an angled face oriented to direct the drill bit in a specific direction off the main well bore where one desires to form the lateral or branch well bore. First, the whipstock directs a special mill to create a “window” or “milled casing window” through the side of the casing of the main well bore. The next step is to go back with a drill bit to complete the lateral or branch well bore through the window. After drilling the lateral well bore, the whipstock is retrieved from the well leaving the main well bore and lateral well bore(s) open.
If re-entry to the lateral well bore is required, the whipstock is typically located in place in the main well bore, and used therein, using an “orienting collar” positioned in the original casing string. The orienting collar ensures that the whipstock will relocate at the exact place and orientation on subsequent runs.
Multiple lateral or branch well bores may be drilled using the same method, each requiring an orienting collar which is positioned in the main well bore so that the whipstock can be positioned and oriented where each lateral well bore is to be drilled. Prior to running the casing string, the orienting collars must be “timed”, that is, properly circumferentially oriented within the main well bore, so that the lateral well bores are drilled in the preferred directions relative to each other.
After the lateral well bore(s) are drilled, the multilateral well will have a main well bore and lateral(s) or branch well bore(s) drilled off of the main well bore. There will be a need to reenter each of the well bores at a later date in order to provide “intervention” services such as fracturing, stimulation or cleanout which require mechanical and pressure integrity within each well bore. Consider, for example, the process involved in order to fracture stimulate each of the bores of a multilateral well, which is a common procedure to enhance production. The workstring is first positioned into the main well bore to fracture the formation, followed by repositioning the workstring into each of the lateral well bores for fracturing each respective formation. With current technology, in order to access each respective lateral well bore, the operator must reinstall the whipstock in the predetermined position in the main well bore. When the operator wants to enter a different lateral well bore, the operator must completely pull the workstring out of the well, and reinstall the whipstock in the new position and rerun the workstring. In fact, each time the operator wants to enter a lateral well bore or the main well bore, the workstring must be removed, the whipstock must be repositioned and the workstring must be redeployed. This adds up to a considerable amount of rig time in performing these operations. In addition, companies that provide support services, such as pump companies, are standing idle waiting for these repositioning operations to complete. During this time, the operator is required to pay the ancillary service companies to stand by, or risk losing their services to another operator resulting in considerable delays in the project. As such, the well operator bears a considerable cost in order to reap the benefits of multilateral completions.